Communications network

ABSTRACT

In a label switch communications network, a third level of label is employed in conjunction with a dynamic multiplex constraint-based routed label switched path (CR-LSP) in order to achieve implicit switching at nodes within the network. Implicit switching occurs when a switching function takes place at a node without the need for any control function being required at that node. A three-layer label stack provided at the edge of the network achieves end-to-end connection oriented behaviour with guaranteed Quality of Service. The use of the three-layer label stack concentrates the control of the network to the two edges of the network and a single central switching stage of the network.

FIELD OF THE INVENTION

This invention relates to arrangements and methods for the switching orrouting of traffic in a communication network.

BACKGROUND OF THE INVENTION

Traditionally, two types of legacy telecommunication networks have beendeveloped. The first type of legacy network is connection oriented andis used for the transport of narrow band voice traffic, typicallycarried in TDM frames. Such networks comprise for example synchronous orplesiochronous networks. The second type of legacy network isconnectionless in nature and is used for the transport of broad bandpacket or cell-based data traffic. Such packet traffic includes forexample Internet protocol (IP) traffic. There is currently a drivetowards unified networks which provide end to end transport for bothvoice and data services, and to this end the use of asynchronoustransport has been introduced. This of course introduces the problem ofsupporting different protocols over a common network.

Asynchronous Transfer Mode (ATM) is the technology specified by theITU-T as a broadband network technology suitable for all applications.For Internet protocol traffic however, ATM has proven to be less thanfully effective at supporting Layer 3 routed applications, such asrouted virtual private networks. This has led the IRTF (InternetResearch Task Force) to specify multi-protocol label switching (MPLS) asa technology which inherits the desirable characteristics of ATM but isbetter matched to the Internet protocol. In particular MPLS provides aframe merge function in which data frames received from multiple sourcesare captured and sent out with a common label. This is key to support ofInternet protocol Layer 3 Routed services. Service providers wouldideally prefer a single network technology to support all of theservices that they provide as this would achieve the lowest possibleoperational cost.

A particular problem with the introduction of a multi-service network isthat of accommodating the various transport protocols and, inparticular, that of providing end to end quality of service guaranteesfor high priority traffic such as voice. In particular, there is a needto provide a network that can carry both data and voice traffic at alocal, national and international level while utilising a commontransport protocol. A further problem with such a network is that ofreal time management of the virtual public/private networks that areestablished within the network. At present, each VPN manager requires adetailed knowledge of the network topology. In a large network this is avery significant operational task.

SUMMARY OF THE INVENTION

An object of the invention is to minimise or to overcome the abovedisadvantages.

According to a first aspect of the invention, there is provided a methodof routing an information packet over a label switched path betweenfirst and second end stations in a virtual private network defined overa network arrangement comprising a hierarchical arrangement of first,second and third levels of routers, the method comprising attaching tothe information packet at a network edge a sequence of first, second andthird labels indicative of a corresponding concatenated sequence oflabel switched path sections within the virtual private network, eachsaid path section extending between a pair of said routers.

According to another aspect of the invention, there is provided acommunications multi-service network comprising: a plurality of nodesinterconnected via quality of service capable tunnels and incorporatinga frame-mode label switched (MPLS) architecture, wherein end-to-endcommunications having a predetermined quality of service are provided bydefining at the network edge a label stack of first, second and thirdlabels for delivering packets through a sequence of said tunnels definedby the label stack.

According to a further aspect of the invention, there is provided acommunications multi-service network incorporating a plurality ofdynamic multiplex constraint based label switched paths defining qualityof service capable tunnels, each said path comprising a second layerconstraint based label switched paths constrained within two first-layerconstraint based label switched paths.

In our co-pending application Ser. No. 09/624,123 (11862ID Mauger) theuse of a two-layer MPLS network in order to simplify the management ofVirtual Public/Private Networks (VPN) is described. In this application,the use of a three-label stack provides connection oriented behaviourfor voice traffic whilst retaining strict edge control analogous tostandard IP network operation. The use of a three layer, five stagehierarchical network of routers enables the technique to be employedover an international or global network.

In a preferred embodiment, the invention provides a system in which afive-stage switching network is configured to allow scaling to thelargest sizes required by any network operator for IP networking,Session Switched Multimedia, PSTN or any other service in a Multiservicenetwork architecture.

In a preferred embodiment, the Common Open Policy Service (COPS)protocol is used to push MPLS Label Switched Paths (LSP) to establish afive-stage network and to establish end-to-end QoS capable connections.

In a further embodiment of the invention, there is provided amulti-service communications network incorporating at least one dynamicmultiplex label switched path comprising a second layer constraint-basedrouted label switched path multiplexed into two first-layerconstraint-based routed label switched paths.

The resource availability of the second-stage layer 1 CR-LSPs may beadvertised periodically to the first-stage LSRs such that the resourceavailability may be utilised in DM-LSP path selection.

Advantageously, the individual dynamic multiplex label switched paths(DM-LSPs) have no pre-defined traffic contracts but instead areconstrained by the traffic contracts of the first layer constraint-basedrouted label switched paths (CR-LSPs) in which they are contained.

In a preferred embodiment of the invention, we employ a three-layerlabel stack at the edge of the network in order to achieve end-to-endconnection oriented behaviour with guaranteed quality of service. Wehave found that the use of the three-layer label stack is sufficient tominimise the control of the network to the two edges of the network anda single central switching stage of the network. In this manner thereal-time control constraints placed on the second and fourth stages ofthe network are removed thus enabling these stages to scale to extremelylarge capacity.

Advantageously, a virtual private/public network is defined withmultiple stages of constraint-based routed label switched paths.

MPLS has been defined by the IETF so as to be independent of theunderlying transport mechanism. Mappings on to ATM have been defined aswell as frame-mode networks using HDLC (High-level data link control)based or other forms of frame transport.

MPLS includes the concept of stacked labels; this allows a network tooperate at multiple layers. For instance a first label in the stack canrelate to a traffic trunk. A switch which only swapped this first labelwould handle the traffic trunk transparently. A switch which popped thefirst label, swapped the second label and pushed a new first label wouldbe switching a service instance between two traffic trunks.

In our arrangement and method, a third level of label is employed inconjunction with a dynamic multiplex constraint-based routed labelswitched path (CR-LSP) in order to achieve implicit switching at certainnodes within a network. Implicit switching occurs when a switchingfunction takes place at a node without the need for any control functionbeing required at that node. Such an implicit switching functionprovides the advantages of simplifying the overall control architectureof the network and minimising the real-time processing requirements onthose nodes that perform the implicit switching function. This enablesvery large scale nodes to be implemented while maintaining theflexibility of having switching points at those nodes.

Advantageously, a bandwidth allocation mechanism is used topre-allocate, on a predictive or as needed basis, capacity within thesecond-stage Layer 1 constraint-based routed label switched paths suchthat dynamic multiplexed label switched path selection is deterministic.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of an exemplary virtual public/privatenetwork according to a preferred embodiment of the invention;

FIG. 2 shows the construction of an abstract node employed in thenetwork of FIG. 1 and illustrates the network construction in furtherdetail;

FIG. 3 shows an exemplary Layer 1 management and bearer controlarchitecture;

FIG. 4 illustrates a virtual public/private network information model;

FIG. 5 illustrates the concept of a Dynamic Multiplex—Label SwitchedPath,

FIG. 6 illustrates a virtual public/private network controlled by athree-label stack according to a preferred embodiment of the invention,

FIG. 7 illustrates the use of the COPS push mechanism to establish MPLSpaths.

FIG. 8 illustrates the label processing functions at each node of FIG. 6

FIG. 9 illustrates an embodiment of FIG. 6 demonstrating its scalabilityto a large network,

FIG. 10 illustrates the control functions of FIG. 6 to guaranteeconnection oriented behaviours of the end-to-end path.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIG. 1, which is introduced for explanatory andcomparative purposes, this figure illustrates in highly schematic forman exemplary virtual public/private network (VPN) deployed nationally orregionally in order to provide session switched multimedia services on aterritorial basis. The network comprises a number of service nodes 11,located at the main centres of population, inter-linked via a network ofcore nodes by quality-of-service (QoS) capable tunnels 12. Theconstruction of the core network will be described below. In FIG. 1,only one core node 18 is shown in the interests of clarity, but it willof course be appreciated that the network will incorporate a pluralityof core nodes. Access to the network from user terminals 13 is providedvia media gateways 14 each serving to one or more service nodes 11.Traffic is transported on constraint-based routed label switched paths(CR-LSP) 15 established between respective gateways. The network carriespacket traffic, each packet 18 comprising a payload and first and secondlabels (Label1, Label2) indicative of the path over which the packet isto be routed.

CR-LSPs (constraint-based routed label switched paths) are deployedbetween the service nodes 11 of the network. Services such asinter-active voice, requiring strict QoS guarantees are supported byend-to-end CR-LSPs 15 as illustrated in FIG. 1. To take a simple exampleof QoS support, if all of the CR-LSPs at both traffic-trunk level andend-to-end are constant bit rate, then the performance of the end-to-endCR-LSP can be substantially equivalent to ATM-AAL1 (AsynchronousTransfer Mode Adaptation Layer One) assuming a typical 48-bytepacketisation.

The IETF has defined two protocols for the establishment of CR-LSPs.These protocols are RSVP-Traffic Engineering, and Constraint-routedLabel Distribution Protocol. CR-LSPs (constraint-based routed labelswitched paths) are point-to-point paths between designated networknodes. Such paths are each assigned a traffic contract which, insuitable carrier strength implementation, will be policed forconformance. We prefer to employ the CR-LDP protocol, but it will beappreciated by those skilled in the art that the RSVP-TE protocol hasequivalent functionality and can be used to serve the same purpose. Sucha CR-LSP has an LSPID (label switched path identifier) which can be usedto specify a hop in a CR-LDP request. In such a case the new CR-LSP willbe multiplexed into the specified CR-LSP and allocated a second levellabel. It is therefore possible to specify within the network of FIG. 1a virtual public/private network (VPN) with multiple stages of firstlevel CR-LSPs and to provide end-to-end services having a CR-LSP trafficcontract by multiplexing further CR-LSPs into a set of appropriate firstlevel CR-LSPs.

A feature of the constraint based routed label distribution protocol(CR-LDP) employed in the network of FIG. 1 is the use of an “abstractnode” to define routing constraints. An abstract node consists of asub-network of real nodes (core nodes) over which the constraint basedrouted label distribution protocol is allowed to select any availablepath to achieve a requested connection. Thus in a path specified as(real node A—abstract node B—abstract node C—real-node D) there may bemultiple real nodes in each of the abstract nodes, and there may also bemultiple trunks between the abstract nodes. This concept of abstractnodes simplifies the management of a VPN as the network manager onlyrequires a view of the network at the abstract node level and does notrequire detailed view of the construction or internal operation of anabstract node.

Referring now to FIG. 2, which is also introduced for explanatory andcomparative purposes, this depicts in schematic form a portion of thenetwork of FIG. 1. FIG. 2 is a representation of a simple network in itsabstract node form, together with a possible real network realisation ofone of the abstract nodes.

The network represents groups of multiple service nodes (SN) 11 eacharranged around a respective abstract node (AN) 22 in each of fourlocations. One of the abstract nodes 22 is shown in detail to illustrateits construction from a sub-network of four core nodes (CN) 18 withmultiple transport links 23 therebetween. In the network of FIGS. 1 and2, an abstract node is defined by an IP address prefix, and all corenodes which include that prefix in their IP address are treated as partof that abstract node. It will of course be understood that an abstractnode may be constructed from some other number of core nodes. Further,abstract nodes can have a temporary, semi-permanent or permanentexistence depending on the network requirements.

Constraint based routed label switched paths 15 are deployed betweenservice nodes 11 via the appropriate intervening abstract nodes 22.

In the arrangement of FIGS. 1 and 2, it is relatively simple for amanagement system controlling the real network to produce an abstractnode version of its information model for use on a super-ordinatenetwork manager. It is also relatively easy to produce a graphicalrepresentation of such a network and to specify traffic trunks bydefining paths between service nodes and passing through abstract nodes.These graphical paths can then be used to automatically construct CR-LDPrequests to establish the traffic trunks. CR-LDP can run on an existingconstraint-based routed label switched path (CR-LSP) to renegotiate thetraffic contract so that the technique provides for near real-timecreation of VPNs as well as flexible service level agreements which canbe modified e.g. on a diumal basis or on any basis which suits thecustomer traffic profile.

A management and bearer control function for the Layer 1 physicalnetwork of FIGS. 1 and 2 is illustrated in FIG. 3. This figure shows byway of example a simple network based on a group of core nodes 18,constituting an abstract node 22, and service nodes 11. The real networkhas a management system based on a hierarchical structure of elementmanagers 31 and (sub) network managers 32. The (sub) network manager 32is responsible for constructing the abstract node information modelrepresentation of the network, which information is passed to asuper-ordinate manager 33. A sub-ordinate manager 38 provides virtualswitch management to perform fault, configuration, accounting,performance, and security management. The super-ordinate manager 33 isused for defining VPNs and placing traffic trunks to realise those VPNs.The super-ordinate manager also creates, modifies and deletes virtualswitches. Traffic trunk requests are passed to bearer control Layer 1(34) to initiate the CR-LDP process. This is the interface point forMPLS Layer 1 Bearer Control for which the common open policy serviceprotocol (COPS) is preferred.

The information model illustrated in FIG. 4 for the sub-network manager32 is also simplified in that only the Layer 2 virtual switches (VS) 41are visible. These virtual switches are configured with access ports 42to which users are connected and traffic trunks 43 configured end-to-endand provisioned with SLAs.

Referring now to FIG. 5 the concept of a Dynamic Multiplex Label SwitchPath (DM-LSP) according to a preferred embodiment of the invention isillustrated. In the exemplary network of FIG. 5, a hierarchical threelayer arrangement of local nodes 51 a, regional nodes 51 b andinternational nodes 51 c is provided, each node comprising a labelswitched router. Within the three-stage network of MPLS label switchedrouters (LSR) a mesh of Layer 1 label switched paths (LSPs) 55 isestablished. As described above, it is possible to define theconstraints for a new label switched path (LSP) in terms of existingLSPs in which case a Layer 2 LSP is established and a second level labeldefines the embedded CR-LSP. In the DM-LSP arrangement illustrated inFIG. 5, a third level label is defined which relates to one of a numberof sessions which can be dynamically multiplexed onto the same labelswitched path (LSP). The DM-LSP 57 itself has no explicit trafficcontract, but is instead subject to the following constraint. A newsession may be multiplexed onto the DM-LSP 57 if and only if theresource constraints of the first-stage and second-stage Layer 1constraint-based routed label switched paths (CR-LSPs) are satisfied.The checking of these constraints can be performed in the first andthird stage LSRs which have full visibility of the resources committedto the first-stage and second-stage Layer 1 LSPs respectively. Thesecond-stage (central) LSRs 51 b perform an implicit switching functionin that session may be dynamically routed between first and third stageLSRs using any available Layer 1 CR-LSPs, but the second stage LSRs arenot involved in the control process. This simplifies the overall controlarchitecture for the network, and minimises the real-time processingrequirements on these second (central) stage LSRs enabling them to scalesignificantly, yet still maintains full switching flexibility. FIG. 5also illustrates a number of LSRs which are used to route the Layer 1CR-LSPs. These are additional network stages that may be required forthe traffic management of large numbers of VPNs. They need not bedirectly involved in the operation of the DM-LSPs. The establishment ofa DM-LSP may be implemented in CR-LDP. CR-LDP using the label requestmessage to establish CR-LSPs. Within this message, notification thatthis is a DM-LSP may be signalled explicitly by defining a type lengthvalue (TLV) field that conveys this information. Alternatively, anexisting traffic TLV may be used by setting the traffic contractparameters (Peak Data Rate etc.) to null values. On receipt of thesenull values, the receiver nodes are able to infer that, as no trafficcontract is defined yet although the new CR-LSP is to be establishedwithin first-layer CR-LSPs with traffic contracts, then this requestmust be for a DM-LSP. Those skilled in the art will recognise thatsimilar mechanisms may also be defined for RSVP-TE.

The ingress point to the DM-LSP (the first stage LSR 51 a) has noinherent visibility of the available resource within the second-stageLayer 1 LSP, and thus requests to establish new sessions upon the DM-LSPmay be denied due to insufficient resource within the second stage(egress) Layer 1 ER-LSP. The probability of denial may be significantlyreduced if the third-stage (egress) LSR periodically advertises theavailable resources (within the second stage Layer 1 LSR) to the firststage LSRs. This resource information enables the first stage LSRs toselect DM-LSPs with a higher probability of success. Alternately, theprobability of denial may be eliminated substantially entirely byemploying a mechanism whereby the second-stage Layer 1 CR-LSP bandwidthis pre-allocated to DM-LSPs according to current (and predicted future)needs. To implement this latter mechanism, the first stage LSR sendssignalled requests to the relevant third-stage LSR asking for anadditional allocation of bandwidth to a particular DM-LSP. This requestwill be granted provided bandwidth is available and the request meetsthe policy constraints set by the network. An equivalent process is usedto relinquish capacity when that capacity is no longer required. Asimple bandwidth management function implemented within the third stage(egress) LSR can be used to perform either of these two mechanisms.

An exemplary five-stage virtual private/public network (VPN) withthree-layer label control is illustrated in FIG. 6. The networkcomprises a hierarchical or layered structure of local routers 61 a,local tandem routers 61 b and national tandem routers 61 c. Asuper-ordinate manager 60 is responsible for configuring one or morevirtual private/public networks (VPN) within the network structure ofFIG. 6. This VPN configuration is performed by defining the Layer 1label switched paths (LSPs) in terms of service level agreements andconstraints for their routing through the network. This information isformulated as a COPS command which is pushed down to the label switchedrouter (LSR) which forms the ingress of the requested CR-LSP. Thesuper-ordinate manager 60 pushes the COPS commands to an admissionmanager (AM) 64 disposed in media gateway controller 65, which admissionmanager records resources available for use in service requests. Theadmission manager 64 then pushes the COPS messages down to the LSRswhere these messages are used to invoke RSVP-TE or CR-LDP sessions inorder to establish the virtual private/public network (VPN). Thesuper-ordinate manager 60 then establishes a mesh of DM-LSPs (dynamicmultiplex label switched paths) between all of the local label switchedrouters (LSRs) and all of the National Tandem LSRs. In addition to theadmission manager function, simplified resource managers uniquelyassociated to the third stage core LSRs (National Tandems) may be usedto control the allocation of layer 1 LSP bandwidth to the DM-LSPs in themanner described above.

The above process establishes a network in which a CR-LSP between anytwo Local LSRs, can be specified by a pair of DM-LSPs. For a full meshconfiguration, there are as many alternative routes between each pair ofLocal LSRs as there are national tandem LSRs deployed in the network.When a media gateway controller wishes to establish a session with QoS(quality of service) guarantees it requests its associated admissionmanager. A session request may be initiated directly by a sessioncontrol protocol such as Q1901 or SIP, or the request may be initiatedas a result of intercepting an RSVP message. Communication between themedia gateway controllers (MGC) uses a protocol which is able to tunnelconnection control information such as Q1901, SIP or RSVP. Theconnection control information which is tunnelled between media gatewaycontrollers comprises a list of LSP-IDs. In the forward direction, thislist contains a set of candidate DM-LSPs which are suitable to provideaccess from the first-stage to third-stage LSRs (Local to NationalTandem). A candidate DM-LSP is defined as a CR-LSP which the originatingAM believes may have available resource to accommodate the sessionrequest.

In the reverse direction, the LSP-ID list comprises a list of the twoDM-LSPs that the far-end admission manager has chosen for the sessionrequest. This list comprises one of the candidate DM-LSPs offered by theoriginating admission manager plus a DM-LSP that will provide theconnection from the third to fifth stage LSR (National Tandem to Local).The scheme may be operated separately for each direction of transport orbi-directional operation may be chosen. The five-stage network issufficient for long distance or global traffic. Fewer stages would berequired for local services.

Once a DM-LSP (dynamic multiplex label switched path) pair-set has beennegotiated, the end-to-end connection is established by the originatingmedia gateway controller. This gateway controller uses e.g. H.248 tocommunicate with the originating media gateway and defines both theingress logical port that connects the terminal to the media gatewaytogether with a bearer package characterising a path across the network.This bearer package contains the first stage LSR IP address, the LSP-IDfor the DM-LSP that connects the first to third stage LSRs, the LSP-IDfor the DM-LSP that connects the third to fifth stage LSRs and the IPaddress of the terminating media gateway. This last address will eitherhave been signalled as part of the normal inter-MGC call controlsignalling, or it could be tunnelled as part of the path negotiationprocess just described. The originating media gateway uses the bearerpackage to initiate an end-to-end CR-LDP label request message thatestablishes a path from media gateway to media gateway. In parallel, theterminating media gateway controller issues an H.248 command to connectthis path to the logical port that connects the media gateway to thefar-end terminal thus establishing the end-to-end session. The CR-LDPlabel request message will explicitly cause the bandwidth capacitycontrol functions to be executed on the first, third and fifth stageLSRs (Local, National Tandem, Local). Thus the connection will berejected if bandwidth is not currently available. This eliminates thepotential for race conditions or any inaccuracies in bandwidthcontrol/advertisement mechanisms. The QoS of existing sessions is alwayspreserved.

In the media gateway-initiated path reservation mechanism describedabove, the media gateways are explicitly informed of the LSP-IDs used inthe core network. If the media gateways are not fully trusted parties,then from a security perspective it would be advantageous to hide thesecore LSP-IDs from them and the following alternative reservationmechanism achieves this.

In this alternative embodiment, a pool of LSPs is pre-establishedbetween the media gateways and the Local LSRs. This LSP pool iscontrolled by the super-ordinate manager as part of the initial VPNestablishment. The admission managers are given visibility of these LSPs(through their LSP-IDs) and control over their allocation.Path-negotiation occurs as before to select a pair of DM-LSPs, but, oncechosen, the end-to-end connection is reserved in the following manner.The originating MGC uses H.248 to create a connection between theterminal and the first-stage LSR via one of the pre-configured LSPs thathas been selected by the admission manager and is identified by itsLSP-ID. The media gateway controller then use COPS to push down theconnection between the first stage LSR and the fifth stage LSR. The COPSpush will thus contain the incoming LSP-ID (MG to Local) plus theLSP-IDs for the DM-LSP pair-set. The first-stage (Local) LSR uses CR-LDPto establish a path across the core-network to the fifth stage LSR. Inparallel the terminating media gateway controller will have issuedsimilar H.248 commands to the terminating media gateway and a COPS pushto the fifth-stage LSR to enable the end-to-end connection to becompleted. The terminating (fifth stage) LSR needs to be able tocorrelate the CR-LDP label request message with the COPS push message sothat it is able to connect the path across the core network with thepath to the terminating media gateway. This may be performed implicitly(i.e. the LSR knows that the next CR-LDP request that it receives from agiven first-stage LSR correlates with the most recent COPS push messageor explicitly (in that a unique matching identifier is contained in bothCOPS and CR-LDP message). The latter mechanism may be achieved inseveral ways. Our preferred method is to pre-allocate a set ofthird-layer LSP-IDs that are visible to the admission manager. Duringpath negotiation the admission manager selects an unused third-layerLSP-ID and includes this ID with the candidate DM-LSP LSP-ID. Once thepath is negotiated, both COPS pushes contain this LSP-ID. Thefirst-stage LSR uses this LSP-ID to identify the third-layer LSP-ID inthe Label Request Message (it is the ingress LSRs role to specify a newLSP-ID for each new CR-LSP). The fifth stage LSR can then correlate thisto the relevant COPS request.

The process of COPS push allows the policy being applied to a particularcontrolled flow on an MPLS router to be asynchronously updated. That is,the MPLS router is told how to change the treatment it applies to theflow, without first asking to change it. This process is enabled by theuse of ClientHandles to identify the flow.

When the path for a new flow is received at an admission manager, a COPSDecision (DEC) message is pushed, that uses the ClientHandle associatedwith the outermost LSP. This naturally performs the selection of thefirst layer ER-LSP. Contained with in this DEC is the list of paths overwhich the flow is to be routed. This list will include the LSP-ID of thenear-end dynamic multiplex, the LSP-ID of the far-end dynamic multiplexand the LSP-ID of the connection from the far-end local switch to thedestination media gateway.

To enable the transfer of this information, we have defined a new COPSSpecific Object. This is shown in FIG. 7. The object conforms to theexisting COPS Specific Object pattern and has a CNum of 40 and Ctypeof 1. The CNum is the identifier for the object, and the CType is theinstance of the object. The Object contains the list of LSP-IDs for theflow in the order in which they are to be used. Therefore LSP-ID 1indicates the near-end dynamic multiplex and will be translated at theLocal LSR into a two-tier label stack. Note that although theClienthandle identifies the layer 1 trunk, this trunk and the dynamicmultiplex share the same LSP-ID space at the local router and thereforeLSP-ID 1 can easily identify the correct label stack. LSP-ID 2 willcontain the LSP-ID of the second dynamic multiplex and LSP-ID 3 willcontain the LSP-ID of the last hop from the far-end Local LSR to the MG.

These next two values are the full 48-bit LSP-IDs. In order that thesetwo values should be copied in the same order into each packet in thisflow as defined above, they must undergo suitable translation. As isillustrated in FIG. 10, each LSP-ID consists of a 32-bit IP address anda 16-bit LSP number. It is the 16 bit LSP number that is of interest soeach LSP-ID must have the IP address removed and replaced with 4 leadingzeros. This makes use of the fact that inserting leading zeros on abinary number leaves the value of that number the same i.e. 1101=00001101.

With this translation performed, the LSP-IDs are inserted in the sameorder as they occur in the COPS message, into the header of each packetin this flow at the Local LSR. That is, LSP-ID 3 should be the innermostof the labels. Once this is successfully completed, a Report State (RPT)message is returned indicating that the new session has beensuccessfully installed.

Once reservation is complete the session can begin. The originatingmedia gateway performs the function of mapping incoming (IP) packets andappending a single label to these packets prior to forwarding to thefirst-stage LSR. The first-stage LSR terminates the label and uses thisas an index to push a 3-label stack onto the payload. The three labelscomprise: a third-layer session label a second-layer DM-LSP label (forrouting from first to third stage LSRs) and the first-layer label. Atthe second-stage LSR (Local Tandem) the first-layer CR-LSP isterminated, the second-layer label is used to identify the correctsecond-stage Layer 1 CR-LSP and its label pushed onto the label-stack.At the third-stage LSR (National Tandem) the second-layer DM-LSP isterminated, the third-layer label being used to index the correspondingLayer 1 and Layer 2 labels to forward the session to the next stage. Theaction at the fourth stage is analogous to the action at the secondstage LSR. At the fifth stage LSR the layer 3 label is swapped for thecorresponding label to forward the connection from the fifth stage LSRto terminating media gateway. The terminating media gateway terminatesthe MPLS stack and routes the packet to the terminating terminal.

The label processing in each of the five nodes is illustrated in moredetail in FIG. 8 which also shows how the optional use of penultimatehop popping can be used to improve bandwidth efficiency. Referring toFIG. 8, the Local LSR receives a packet with the label assigned to theMG-LSP A at configuration time. The payload is retrieved and threelabels are pushed: Tunnel A Label/DM-LSP A Label/Session Label. Assumingpenultimate hop popping, then the packet received by the local tandemnode is headed by the DM-LSP A Label. As this is the penultimate nodefor the DM-LSP A its label is popped. The payload and remaining labelsare then sent out on Tunnel B with Tunnel B label. Again withpenultimate hop popping the packet received by the national tandem isheaded by the session label which is used to identify DM-LSP B and thelabel pair Tunnel C. These two labels are pushed above the sessionlabel. At the distant local tandem the DM-LSP B Label is recognised as apenultimate hop for DM-LSP B and is popped. The payload and remaininglabels are sent out on Tunnel D with Tunnel D Label. At the destinationLocal LSR the packet is headed by the session label which is consumed inidentifying MG-LSP B and the packet is delivered to the media gatewaywith MG-LSP B Label which was established when MG-LSP B was configured.

By analogy with the PSTN five stages of switching appear to be necessaryfor QoS capable networks leading toLocal/Local-Tandem/National-Tandem/Local-Tandem/Local routing fornational services andLocal/Local-Tandem/International-Tandem/Local-Tandem/Local routing forinternational services.

By way of example of the efficacy of the techniques described above,consider a carrier having 50 million customers in the USA and a further50 million customers in the rest of the world with 0.1 Erlang of sessiontraffic per customer. Assume that typically 40% of traffic is longdistance and 10% of traffic is international. The United States networkcould be organised with e.g. five hundred local nodes with typically100,000 customers each. The Local-Tandems could be disposed in e.g.fifty groups with two switches in each group dedicated to National andInternational traffic. Approximately one hundred national-tandems andtwenty five international-tandems would be deployed throughout the worldto provide a global network. In this scheme the local nodes wouldtypically support only 10,000 Erlangs and no tandem node would need tosupport more than 25,000 Erlang of session traffic. These are trivialamounts of traffic by modem standards and this readily demonstrates theflexibility and efficacy of the five-stage network described herein. Theconnectivity of such a network is illustrated in FIG. 9. The nodes asillustrated are Virtual Nodes, a real physical switch could support anumber of such Virtual Nodes.

The overall control environment for five-stage MPLS networks isillustrated in FIG. 10. Each admission manager associated with an mediagateway controller maintains a regular dialogue with the DM-LSP controlfunctions in the national and international tandems. On a routine basis,the admission manager informs the DM-LSP Control of its currentutilisation of resources on a particular DM-LSP. This allows the DM-LSPControl to evaluate the resource utilisation on the hidden tunnel (i.e.egress from Local LSR to National Tandem or Ingress from National Tandemto Local) for this DM-LSP, and to offer an explicit allocation ofresources to the admission manager for the next control interval.Assuming session holding times equivalent to current PSTN practice ofabout 120 seconds, then control intervals of 10 or 20 seconds would beappropriate. Alternatively the previously described advertisement methodcould be used.

When a session request arises then the AM on the originating side isable to select an MG-LSP A and to nominate candidate DM-LSPs Ax, Ay, Azwhich have sufficient allocated resource for the session (optionally italso identifies the LSP-ID that will be used to establish the new layer3 CR-LSP). The terminating side admission manager is now able to definethe LSP-ID tuple for the connection by inspecting candidate DM-LSPs Bx,By, Bz. After selection, the admission manger offers MG-LSP A/DM-LSPA/DM-LSP B/MG-LSP B. This is then used by the admission manager to pushthe end-to-end connection. If the DM-LSP Control function is cautious inallocating resources to admission managers, then the whole process isdeterministic and the Layer 1 Tunnels need never be overloaded. Theexplicit path reservation mechanism deployed ensures that this is alwaysthe case.

It will be understood that the above description of a preferredembodiment is given by way of example only and that variousmodifications may be made by those skilled in the art without departingfrom the spirit and scope of the invention.

1. A method of routing information packets over label switched paths ina communications multi-service network comprising a plurality of nodesinterconnected via quality of service capable tunnels each having anallocated resource capacity and incorporating a frame-mode labelswitched (MPLS) architecture, wherein end-to-end communications having apredetermined quality of service are provided by: establishing saidtunnels as first level label switched path sections, identified by firstlevel labels; defining at the network edge a label stack of at least asaid first level label and a second level label, said label stackdefining a concatenated sequence of said tunnels; and routing saidinformation packets over said concatenated sequence of said tunnelsusing said label stack.
 2. A method as claimed in claim 1, comprising:establishing a dynamic multiplexed label switched path, identified bysaid second level label, said dynamic multiplexed label switched pathcomprising first level label switched path sections corresponding tosaid concatenated sequence of said tunnels.
 3. A method according toclaim 2, wherein the dynamic multiplexed label switched paths have noallocated resource capacity.
 4. A method as claimed in claim 2, whereininformation packets for a new session are multiplexed onto said dynamicmultiplexed label switched path only if the available resource capacityof said concatenated sequence of tunnels is sufficient.
 5. A method asclaimed in claim 1, wherein available resource capacity of tunnelscorresponding to said label switched path sections is advertisedperiodically to the network edge, and wherein the available resourcecapacity is used to determine path selection.
 6. A method as claimed inclaim 4, wherein a session routed over a said dynamic multiplexed labelswitched path is identified by a third level label in said label stack.7. A method as claimed in claim 6, wherein a bandwidth allocationmechanism is used to pre-allocate, on a predictive or as needed basis,resource capacity within tunnels corresponding to the first level labelswitched path sections such that path selection is deterministic.
 8. Acommunications multi-service network comprising: a plurality of nodesinterconnected via quality of service capable tunnels each having anallocated resource capacity and incorporating a frame-mode labelswitched (MPLS) architecture, wherein end-to-end communications having apredetermined quality of service are provided by: establishing saidtunnels as first level label switched path sections, identified by firstlevel labels; defining at the network edge a label stack of at least asaid first level label and a second level label, said label stackdefining a concatenated sequence of said tunnels for routing informationpackets.
 9. A communications multi-service network as claimed in claim 8incorporating dynamic multiplexed label switched path identified by saidsecond level label, said dynamic multiplexed label switched pathcomprising first level label switched path sections corresponding tosaid concatenated sequence of said tunnels.
 10. A communications networkas claimed in claim 9, wherein said dynamic multiplexed label switchedpath is constrained entirely by the allocated capacity of saidconcatenated sequence of said tunnels.
 11. A communications network asclaimed in claim 9, wherein information packets for a new session arecapable of being multiplexed onto said dynamic multiplexed labelswitched path only if the available resource capacity of saidconcatenated sequence of said tunnels is sufficient.
 12. Acommunications network as claimed in claim 8, wherein available resourcecapacity of tunnels corresponding to said label switched path sectionsis advertised periodically to the network edge, and wherein theavailable resource capacity is used to determine path selection.
 13. Acommunications network as claimed in claim 9, wherein a sessionestablished on a said dynamic multiplexed label switched path isidentified by a third level label in said label stack.
 14. Acommunications network as claimed in claim 9, wherein a bandwidthallocation mechanism is used to pre-allocate, on a predictive or asneeded basis, resource capacity within tunnels corresponding to thefirst level label switched path sections such that path selection isdeterministic.
 15. A communications network according to claim 9,wherein the dynamic multiplexed label switched paths have no allocatedresource capacity.